Increasingly, electric motors are used to propel vehicles. Vehicles in which electric motors provide the propulsion together with motors of other designs, such as internal combustion engines, as well as vehicles in which only electric motors are used for propulsion, are customary.
In the course of further development and the reduced dimensions of the electric motors that this has brought about, it is possible to use, instead of one powerful centrally arranged electric motor, which takes effect on at least one drive axle, several smaller electric motors, such that one electric motor can be assigned to each drive wheel. These electric motors can be placed near the corresponding drive wheel, and the distance over which the force must be transferred from the drive motor to the drive wheel can be kept short.
Since these electric motors also produce heat in addition to the kinetic energy dedicated to propelling the vehicle, it is necessary to cool the motor in order to prevent damage to the motor. Cooling devices are used for cooling. These devices absorb the heat given off by the electric motor and remove such heat from the electric motor. So, for example, a cooling fluid is led to the electric motor by means of a pump; the fluid is warmed up by the electric motor and the waste heat of the electric motor is at least partially absorbed by the fluid. The cooling fluid that is warmed up in such a manner is moved away from the electric motor, and the waste heat is removed from the electric motor and the electric motor is thus cooled.
This prevents the overheating of the motor, and the electric motor can be operated at high capacity over a long period of time.
In order to ensure a controlled supply of the electric motor with cooling fluid, the cooling fluid is typically brought to the electric motor by means of one or more cooling fluid supply lines, and led back into a reservoir by means of a cooling fluid discharge line. From the reservoir, the absorption of the cooling fluid may in turn take place by means of the cooling fluid supply line. Thereby, the cooling of the cooling fluid can take place in the cooling fluid reservoir or in the cooling fluid supply lines or discharge lines. Moreover, a separate cycle for the cooling of the cooling fluid is conceivable. At the electric motor, the cooling fluid is heated by the electric motor. Such cooling devices comprise, for example, a cooling fluid supply line, a cooling fluid discharge line, a cooling fluid pump, a heat exchange area for absorbing the heat from the cooling fluid, and a cooling fluid reservoir to make the cooling fluid available. However, such cooling devices represent an additional weight and require additional space, thus increasing the overall dimensions and overall weight of the drive and thus of the vehicle as a whole.